How to: Sit down with your knees bent and feet flat on the floor in front of you (a). Place your right ankle on top of your left thigh and flex your right foot (b). Put your hands behind your body, fingertips facing away from your body and begin to press your hips toward your heels until you feel a stretch through your outer left hip. Keep your back tall and chest open (c). Hold for six to eight breaths, then repeat on the other side.

The term iliopsoas refers to the iliacus and psoas muscles, which are grouped together because they function collaboratively and share a common tendon. The psoas originates from your lower spine, and the iliacus arises from the inside of your hipbone. The muscles come together as they cross through the pelvis and insert on the inner thighbone below the hip joint. The iliopsoas is the most powerful hip flexor.

Grade III (severe): A complete tear in your muscle that causes severe pain and swelling and you can't bear weight on that leg, making it difficult to walk. You've also lost more than 50 percent of your muscle function. These injuries are less common and may need surgery to repair the torn muscle. They can take several months or more to completely heal.
You're more likely to get a hip flexor injury if you've had one in the past, you don't warm up properly before engaging in athletic activity, your muscles are already tight or stiff, or your muscles are weak from being overused. If, while exercising, you try to do too much at once in too short an amount of time, you can also put yourself at risk for a hip flexor injury.
Those are some great stretches! I own a personal training studio in Severna Park, Maryland. Majority of my clients have physical limitations – so it’s important for them to stay flexible. I send these to my clients and even do these exercises for myself. I highly recommend these stretches to anyone, even people without physical limitations. I love the fact these are actually videos and not just stretches because it’s so much easier for people to figure out how to perform the stretches. You guys are the real MVP!
The better you understand anatomy and biomechanics the more effectively you can program exercise for clients who need correction and/or to restore balance between the right and left sides of the body. There are 11 muscles that flex the hip joint. Each of these muscles also has other abilities for movement. For example, tensor fasciae latae also internally rotates the hip and abducts it. Whereas sartorius abducts but externally rotates the hip. The muscles in the human body all overlap each other in their abilities, making it the machine of many movements that it is.
The iliotibial band is a thickening of the fascia lata, the deep fascia of the thigh. Think of it as a thick long ligament like structure that connects the hip to the lower leg along the outside of the thigh. Tightness in the iliotibial band can cause patellofemoral pain, trochanteric bursitis, and friction syndromes at the knee. This is a hip stretch I commonly prescribe to runners and people suffering from knee pain.
Kneel on your mat with your thighs perpendicular to the floor and tops of your feet facing down. Bring your inner knees together. Slide your feet apart so they are slightly wider than your hips and press the tops of your feet evenly into the mat. Slowly sit down between your feet. Use your hands to turn the top of your thighs inward. Then, lean back onto your forearms and slowly lower torso to floor. Hold for at least 30 seconds.

Athletes with marked weakness of the hip abductors will exhibit the classic Trendelenburg gait pattern. Hallmarks of the Trendelenburg gait pattern are depression of the swing phase pelvis (as the stance phase hip abductors cannot resist the pull of gravity on the unsupported side of the body).4,8,13 Athletes often find ways to compensate for a relative weakness, such as with a compensated Trendelenburg gait pattern. With this pattern the athlete exhibits increased deviation of the body in the frontal plane toward the stance leg. This causes a decrease in the moment arm of gravitational forces pulling on the unsupported half of the body and a relative decreased load on the stance phase hip abductors (Table 12-1).8,13

Work on strengthening all of your core muscles and glutes. These muscles work together to give you balance and stability and to help you move through the activities involved in daily living, as well as exercise and sports. When one set of these muscles is weak or tight, it can cause injury or pain in another, so make sure you pay equal attention to all of them.
Like rolling, this is a movement that deserves to be done as often as you can tolerate. Physical therapist and coach Kelly Starrett has written that you should do it for two minutes on each side every half hour. That may be tough to manage, but the point is this: Frequent, long-duration stretches are the only stretches that will have any significant effect on your tissue length and mobility. If you want to improve, you have to commit.
The primary hip flexors are the rectus femoris, iliacus, psoas, iliocapsularis, and sartorius muscles. The rectus femoris muscle has two distinct origins proximally: the direct head and the reflected head. They originate at the AIIS and the anterior acetabular rim (in close proximity to the anterior hip capsule), respectively. The tendinous fibers of the rectus femoris coalesce distally and become confluent with the other quadriceps musculature in the thigh. The quadriceps consists of four distinct muscles: 1) the vastus intermedius; 2) the vastus lateralis; 3) the vastus medialis; and 4) the rectus femoris. The rectus femoris is the only quadriceps muscle that traverses both the hip and the knee joint. The rectus femoris is a powerful hip flexor, but it is largely dependent on the position of the knee and hip to assert its influence. It is most powerful when the knee is flexed, whereas significant power is lost when the knee is extended. The rectus femoris is innervated by the femoral nerve (i.e., the posterior division of L2 to L4).
Of course, you know what it feels like to have a tight muscle. But tight hips aren't just uncomfortable—they can lead to all sorts of other aches and pains, especially in the lower back. "People focus on the hips and say their hips are tight, but we don't always think about the fact that the lower back connects to our legs at the hip," Charlee Atkins, C.S.C.S., instructor at Soul Annex in New York City and creator of Le Stretch class, tells SELF. Tight hip flexors make it harder for your pelvis to rotate properly, which can cause your lower back to overcompensate, "and this can be a setup for lower-back injury," Teo Mendez, M.D., an orthopedic surgeon at NY Orthopedics who focuses on operative and non-operative management of sports-related injuries, musculoskeletal injuries, and arthritis, tells SELF.